| Clean combustion and pollutant emission control of carbon-based fuels such as coal and biomass are major issues of high quality development in our country.With the rapid development of economy and society,the consumption of coal and other carbon-based fuels surges,resulting in increasingly serious air pollution.Among them,nitrogen oxide(NOx)is a major atmospheric pollutant.In recent years,it has become one of the hot spots in the field of energy and chemical industry to study the influence of NOx emission and regulation mechanism generated in the thermochemical conversion process of various carbon-based fuels.Due to the complexity of the chemical structure of each carbon-based fuel and the occurrence state of nitrides,there is no unified understanding of the NOx formation mechanism of fuel type nitrides in different chemical bonding environments in coal and other fuels in the process of pyrolysis,combustion and chemical chain technology.A relatively complete complex reaction network system of fuel-type organic nitrogen in the typical thermochemical transformation process has not yet been established.Therefore,it is of great significance to study the mechanism and process of fuel-type organic nitrides in typical thermochemical conversion process for realizing clean conversion of carbon-based fuels and NOx emission control.Based on the comprehensive research methods of experiment and multi-scale calculation simulation,the reaction behavior of fuel-type organic nitrides in traditional combustion and chemical chain combustion was investigated,the influence mechanism of different characteristic chemical bonding environments on the thermochemical transformation process and mechanism of fuel-type nitrides was analyzed,and a complex reaction network was constructed.The main contents include:(1)Based on the characteristics of chemical bonds of nitrides in carbon-based fuels,the microscopic reaction mechanisms of different nitrogen-containing model compounds in conventional fuel processes and the complex reaction networks of nitrogen conversion were studied.Different coal/biomass samples were collected,and combined with elemental analysis,X-ray photoelectron spectroscopy(XPS),solid NMR and FT-IR characterization,the occurrence forms of organic nitrogen in solid fuel were obtained.Nine different nitrogen microenvironments were selected to perform oxygen-fuel molecular dynamics simulations at different temperatures.The effects of O2 and different temperatures on nitrogen atom distribution,NOx and CO2/H2O release were studied.The depolymerization behavior and chemical bond cracking of nitrogen-containing model compounds during the oxidation process were analyzed by visualization analysis,primitive reaction detection and product reverse tracking methods.The thermal transformation kinetics law was summarized,and the reaction network system of each nitrogen-containing fuel model molecule was obtained.The results show that,through the simulation results,the change trend of main product and main intermediate with the reaction process,the competition of pyrolysis and oxidation,NOx and other main forms are obtained.TG-MS was used to measure the changes in the production of NOx/CO2/HCNO/CNO/H2O/O2 of the above model compounds over time at different temperatures and heating rates,so as to test and modify the proposed transformation mechanism.(2)ReaxFF MD was used to simulate the heat conversion behavior of fuel nitrogen during the chemical looping combustion of copper based oxygen carriers.The molecular number evolution law of main reactants,combustion products,nitrogen-containing intermediates and NOx of pyridine,pyrrole and graphite organic nitrogen at different reaction temperatures was investigated.The ring-opening sites and probability of molecular ring opening caused by pyrolysis and oxidation were calculated.A three-stage thermal reaction network system of pyridine,pyrrole and graphite-type organic nitrogen model molecules in the process of chemical looping combustion was constructed.The results show that CuO oxygen carrier mainly releases O=O at the initial stage and lattice oxygen at the later stage.The higher the reaction temperature,the more NO was released and the more frequent the occurrence of NO2.In the process of chemical looping combustion reaction,there are two main initial ring-opening modes of organic nitrogen model molecules,namely,pyrolytically induced ring-opening,oxygen group attacking nitrogen,and outer carbon atom promoting ring-opening,among which oxidation is the dominant ring-opening mode.The structure of nitrogen-containing thick ring intermediates produced by three different organic nitrogen models in the initial ring-opening reaction was significantly different due to different factors,but most of these intermediate species eventually generated·N and·CN radicals at the end of the chain reaction.·N and ·CN are important precursors of NOx formation,and their conversion to NOx mainly includes:attack by free oxygen groups,adsorption/heterogeneous reaction on the surface of oxygen carrier particles,and REDOX reaction with dissociated CuO fragments.Finally,through the study of the interactive oxygen release process between nitrogen-containing species and oxygen carriers,it is found that CuO oxygen carriers have three main oxygen release pathways,and there are four REDOX reaction stages.The reactive properties of different nitrogen-containing fuel molecules in CLC were evaluated. |
PDF Full Text Request